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Remove duplicate rows in MySQL
...owing columns:
employee (id, first_name, last_name, start_date, ssn)
In order to delete the rows with a duplicate ssn column, and keeping only the first entry found, the following process can be followed:
-- create a new tmp_eployee table
CREATE TABLE tmp_employee LIKE employee;
-- add a unique...
Comparing two collections for equality irrespective of the order of items in them
...valent if they
have the same elements in the same
quantity, but in any order. Elements
are equal if their values are equal,
not if they refer to the same object.
Using reflector, I modified the code behind AreEquivalent() to create a corresponding equality comparer. It is more complete tha...
Merge and interleave two arrays in Ruby
...
This won't give a result array in the order Chris asked for, but if the order of the resulting array doesn't matter, you can just use a |= b. If you don't want to mutate a, you can write a | b and assign the result to a variable.
See the set union documentation ...
Condition within JOIN or WHERE
...sider these two queries:
SELECT *
FROM dbo.Customers AS CUS
LEFT JOIN dbo.Orders AS ORD
ON CUS.CustomerID = ORD.CustomerID
WHERE ORD.OrderDate >'20090515'
SELECT *
FROM dbo.Customers AS CUS
LEFT JOIN dbo.Orders AS ORD
ON CUS.CustomerID = ORD.CustomerID
AND ORD.OrderDate >'20090515'
The f...
How do I delete a fixed number of rows with sorting in PostgreSQL?
...DELETE FROM logtable
WHERE ctid IN (
SELECT ctid
FROM logtable
ORDER BY timestamp
LIMIT 10
)
The ctid is:
The physical location of the row version within its table. Note that although the ctid can be used to locate the row version very quickly, a row's ctid will change if it is...
Using helpers in model: how do I include helper dependencies?
...
To access helpers from your own controllers, just use:
OrdersController.helpers.order_number(@order)
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What are good examples of genetic algorithms/genetic programming solutions? [closed]
...nute-by-minute price data of the S&P500 futures, as well as a specific order (buy or sell) and stop-loss and stop-profit amounts. Each string (or "gene") had its profit performance evaluated by a run through 3 years of historical data; whenever the specified "shape" matched the historical data,...
The type must be a reference type in order to use it as parameter 'T' in the generic type or method
...koverflow.com%2fquestions%2f6451120%2fthe-type-must-be-a-reference-type-in-order-to-use-it-as-parameter-t-in-the-gen%23new-answer', 'question_page');
}
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Using .sort with PyMongo
...er", 1), ("date", -1)])
The reason why this has to be a list is that the ordering of the arguments matters and dicts are not ordered in Python < 3.6
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Explaining Apache ZooKeeper
...hority for writes: in this way writes can be guaranteed to be persisted in-order, i.e., writes are linear. Each time a client writes to the ensemble, a majority of nodes persist the information: these nodes include the server for the client, and obviously the master. This means that each write makes...